How to Troubleshoot an Air Brake System


Tractor trailer trucks use air brake systems. Without the proper operation of the air braking system, the truck will be dangerous to drive and difficult to stop. Proper troubleshooting of the air brake system is a must before you take your truck on the road.

  • Start up the truck and watch the air gauge. There is a horn that will be active until the air pressure is over 100 psi. The air pressure should build to 120 psi and hold if the compressor is working properly.

  • Do a walk around of your truck and listen for leaking air lines and valves.

  • Identify damaged air lines and make repairs as needed. Once you identify valves that are leaking air, check the service manual to identify which valve you are dealing with and what its function is.

  • Make repairs and replace air system valves as needed.

  • Drain the air tanks on both sides of the truck by starting the truck, allowing air pressure to build and opening the hand valve located at the bottom of both air tanks. Turn the valves counterclockwise to open and clockwise to close the valve. You will see a water and oil mixture drain out of the valve. Allow it to drain until no more sludge comes out and close the valve by turning it clockwise.

  • Push in the brake releasing valve and monitor the air pressure gauge for any drop in pressure. If the pressure drops that means one or more of the brake chambers is leaking air and needs to be replaced. Do a visual inspection to determine which one.

Tips & Warnings

  • Wear safety glasses when checking air valves under the truck to prevent dust and debris from getting in your eyes.
  • Do not drive your truck until you are satisfied the air system is working properly and leak free. An air system that is not working as it should can be dangerous to drive because the brakes will not stop properly.

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